1. Field of the Invention
The present invention relates to a closing unit for an injection molding machine.
2. Related Art
The closing unit of an injection molding machine receives the injection mold. It carries out the movements necessary for the closing and opening of the injection mold and produces the forces necessary for the locking and opening of the injection mold. The main components of each closing unit are a stationary plate on the injection side (hereinafter referred to as the injection plate), a movable closure plate, as well as a locking device. One part of the injection mold is clamped on the stationary injection plate while the complementary part of the injection mold is clamped on the movable closure plate. By locking device there is to be understood the device which, upon the injection and further pressing, produces the necessary closing force for keeping the injection mold closed.
Both mechanical locking devices with lever mechanisms and hydraulic locking devices with hydraulic cylinders are known.
The present invention relates to a closing unit with hydraulic locking. In the book "Kunstsfoff-Maschinen-Fuhrer," 3rd edition, edited by Dr. Eng. Friedrich Johannabe, published by Carl Hanser Verlag (Munich, Vienna), 1992 various constructions of closing units with hydraulic locking are described.
In most closing units with hydraulic locking, a force cylinder is developed as a pressure cushion and is arranged on the support plate behind the movable closure plate.
From FIG. 56, page 110, of said book, a closing unit having four hydraulic cylinders on the stationary injection plate is, however, known. The pistons of said hydraulic cylinders are connected rigidly via connecting rods with the movable closure plate. The four hydraulic cylinders produce the required closing force but also, at the same time, carry out the opening and closing movements of the movable closure plate. Since the four hydraulic cylinders at the same time perform a locking function and a displacement function, they must be both of large cross section and have a large stroke and they therefore take up a relatively large amount of space. The four relatively large hydraulic cylinders accordingly substantially impede accessibility to the injection unit and furthermore have a very high consumption of oil. The structural length of the closing unit is substantially greater than the greatest possible distance between the injection plate and the closure plate.
From FIG. 53B, page 108, of the same book, a more compact closing unit, also having four hydraulic cylinders on the stationary injection plate, is known. The four connecting rods are detachably connected by claws at their ends to the corresponding hydraulic cylinder. Opening and closing movements are produced, with connecting rods uncoupled, by high-speed cylinder arranged on the side. The stroke of the four hydraulic cylinders in this construction must accordingly correspond merely to the difference in length between the largest and smallest injection molds. This construction is primarily of interest when the injection molds used all have more or less the same length. If the closing unit, however, is to be used with injection molds of different length, the stroke of the hydraulic cylinders must be relatively large and the closing unit of FIG. 53B has substantially the same disadvantages as the aforementioned closing unit of FIG. 56.